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High(er) Oil Pressure


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So here's a plot from right after my previous oil change (Nov of 2023) and then one from a flight from the recent one.  Looking at them, the oil pressure is only about 3psi average higher, but I have never seen it in the 80s before which is why I noticed it.  Oil temps appear the same on both flights and both pressure and temp are pretty stable for long periods (both of these flights are 2-4 hours).  Weird, but probably nothing...

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This is the recent one below:

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OAT is lower on the bottom plot.   On Lycomings the oil goes through the cooler first, before it gets to the pressure regulator.    The regulator (relief valve, actually), and vernatherm should still work basically the same, but they're not precision devices.   It could even be just the different batch of oil was a bit different in viscosity or something, or some combination of small factors.

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At the Lycoming factory class it was pointed out that higher is always better and anything below 100 psi (115 during start, warm up, takeoff) is fine.

Lycoming considers 160 F to 210 F to be the normal range with 180 F nominal. The lubrication system will begin to drop pressure when the oil temperature reaches 220 F.

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Won't a change in oil viscosity change oil pressure? I notice for instance that my oil pressure is higher when the oil is cold than when it is hot. So if you changed oil weights wouldn't that affect the pressure?

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13 hours ago, gevertex said:

Won't a change in oil viscosity change oil pressure? I notice for instance that my oil pressure is higher when the oil is cold than when it is hot. So if you changed oil weights wouldn't that affect the pressure?

Yes, but they are more/less the same weight once hot (maybe someone uses aeroshell 80?).  I’ve been using Xc 20w-50.  It should be the same as Aeroshell 100 when hot.  Anyway, I used the same oil I normally do.  However if the batch is slightly different, that could do it.

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  • 3 weeks later...

Wonder if your baffling wasn’t as effective on previous oil changes and this time it’s got a good tight fit thus forcing more oil through the oil cooler and cylinder heads making the oil not heat up as much and giving a slightly higher reading?

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On 5/9/2024 at 5:25 AM, Ragsf15e said:

Yes, but they are more/less the same weight once hot (maybe someone uses aeroshell 80?).  I’ve been using Xc 20w-50.  It should be the same as Aeroshell 100 when hot.  Anyway, I used the same oil I normally do.  However if the batch is slightly different, that could do it.

Maybe, in theory,...but when I discussed high oil temps with my A&P his first question was what oil I was using.  FWIW, he said he's seen higher oil temps with multi-viscosity oils than with single weights.  Anecdotal as he didn't have 'hard data' available.

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12 minutes ago, MikeOH said:

FWIW, he said he's seen higher oil temps with multi-viscosity oils than with single weights.

But going from XC 20w-50 to 20w-50 to 20w-50, in theory, should not show any change.  Sure, maybe change over years, but not from a flight yesterday to a flight today after an oil change.  Why the change with no real time between, using the same oil type that has been used over a long period? 

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7 minutes ago, PeteMc said:

But going from XC 20w-50 to 20w-50 to 20w-50, in theory, should not show any change.  Sure, maybe change over years, but not from a flight yesterday to a flight today after an oil change.  Why the change with no real time between, using the same oil type that has been used over a long period? 

@PeteMc

Correct, and no idea why it would be different from one oil change to another with the SAME oil.

If you read the post I was responding to, however, you will see I was addressing the statement "...Xc 20w-50. It should be the same as Aeroshell 100 when hot."

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  • 2 weeks later...
Posted (edited)
On 5/4/2024 at 6:01 PM, EricJ said:

OAT is lower on the bottom plot.   On Lycomings the oil goes through the cooler first, before it gets to the pressure regulator.    The regulator (relief valve, actually), and vernatherm should still work basically the same, but they're not precision devices.   It could even be just the different batch of oil was a bit different in viscosity or something, or some combination of small factors.

To close this out, my oil pressure has returned to where it has always been.  It seems to have happened slowly over the last month.  Was it the warming temperatures or the oil “breaking in”?  I don’t know.  Today i flew at +3 oat at 10,500’ and the oil temp was about 4 degrees warmer than previously (180 vs 184), but the  pressure was back down to 76/77 where I’m use to it.  After the oil change, i was seeing ~-10 oat and maybe 180 oil temp.  The oil now has about 12 hours on it.

Edited by Ragsf15e
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